Due to their low cost and ease of processing/shaping by various means, polymeric materials, which are optionally filled with or reinforced with materials selected from the group of metals, metal alloys, and/or carbon based materials selected from the group of graphite, graphite fibers, carbon and carbon nanotubes, glass, glass fibers and other inorganic fillers, are widely used. Problems encountered with polymeric materials include poor strength, low hardness, low wear and erosion resistance, residual porosity, cracks induced during forming, handling or abuse and susceptibility to degradation by certain fluids (gases, liquids) resulting in undesired swelling, leaching, erosion and cracking.
Applying metal coatings or layers to the surface of polymer parts is of considerable commercial importance because of the desirable properties obtained by combining polymers and metals. Metallic layers/coatings that are strong, hard tough and substantially porosity free can be applied by various commercial process methods including electroless deposition techniques and/or electrodeposition. The metal deposits must adhere well to the underlying polymer substrate even in corrosive environments and when subjected to stress, impact, thermal cycling, erosion and wear, as encountered in outdoor or industrial service. When used in repair/refurbishment of polymer articles a relatively thin net shape metallic coating applied without the use of an adhesive may be desired to maintain the original dimensions.
The prior art describes numerous processes for repairing polymer parts:
Briggs in U.S. Pat. No. 4,568,589 (1986) describes a patch and method of repair of the integrity and/or surface imperfections of a structure which is defective because of accidental damage or flaws during the course of manufacture or subsequent use and handling. The invention relates to the use of a fibrous cloth which is impregnated by a fast curing acrylic-based adhesive composition containing an activator/accelerator that is applied to the faulty work piece and cured at ambient temperature. The improved material provides good adhesion to a wide variety of materials including unprepared metals, painted metals, plastics and moist or oil contaminated surfaces and displays a high impact.
Kipp in US 2008/0008836 (2008) describes a method for enhancing the vacuum integrity and for extending the useful life of a mold-type forming tool operable with negative pressure. The method comprises preparing a surface of the tool to receive a sealing coating thereon; optionally applying a primer material to the surface; applying a sealing coating comprising urea and polyurethane to the surface, and curing the sealing coating to effectuate the bond between the sealing coating and the surface, and to seal the surface.
Presswood in U.S. Pat. No. 4,879,182 (1989) describes a way of sealing a carbon body such as monolithic graphite tooling so that it retains its vacuum integrity through numerous thermal cycles typical of thermoplastic processing. This is accomplished by applying a coating composed of a carbon-filled solution of a polyamic acid to the carbon body surface, and curing the coated body to cause the polyamic acid to imidize into a thermally cured polyimide.
McBroom in U.S. Pat. No. 6,149,749 (2000) describes a patch of fiber reinforced plastics composite material, a repair kit including such a patch and a method of using such a patch and repair kit. The patch is attached to a surface of a fiber reinforced plastics composite structure where damage has occurred. The patch includes fiber reinforcement and plastic matrix materials and the patch contains a series of small apertures to allow the passage of gases and other matter through the patch to prevent entrapped air weakening the repair.
The prior art describes methods for applying metallic coatings to polymer parts:
Lui in U.S. Pat. No. 4,231,847 (1980) describes a method of electrodepositing an alloy of nickel and iron having a low temperature expansion coefficient. The method includes the steps of forming an aqueous electrolyte solution of nickel and iron salts and electrodepositing a nickel iron alloy onto a substrate. Suitable substrates include lightweight graphite materials having a low coefficient of linear thermal expansion.
Various patents address the preparation of grain-refined, strong, metallic layers and articles for a variety of applications:
Erb in U.S. Pat. No. 5,352,266 (1994), and U.S. Pat. No. 5,433,797 (1995), assigned to the same applicant, describe a process for producing nanocrystalline materials, particularly nanocrystalline nickel. The nanocrystalline material is electrodeposited onto the cathode in an aqueous acidic electrolytic cell by application of a pulsed current.
Palumbo DE 102 28 323 (2005), assigned to the same applicant, discloses a process for forming coatings or freestanding deposits of nanocrystalline metals, metal alloys or metal matrix composites. The process employs tank, drum plating or selective plating processes using aqueous electrolytes and optionally a non-stationary anode or cathode. Nanocrystalline metal matrix composites are disclosed as well.
Tomantschger in U.S. 2009/0159451 (2009), assigned to the same applicant, discloses variable property deposits of fine-grained and amorphous metallic materials, optionally containing solid particulates.
Palumbo in U.S. Pat. No. 7,320,832 (2008), assigned to the same applicant, discloses means for matching the coefficient of thermal expansion of a fine-grained metallic coating to the one of the substrate by adjusting the composition of the alloy and/or by varying the chemistry and volume fraction of particulates embedded in the coating. The fine-grained metallic coatings are particularly suited for strong and lightweight articles, precision molds, sporting goods, automotive parts and components exposed to thermal cycling and include polymer substrates optionally reinforced with conductive fibers. Maintaining low coefficients of thermal expansion and matching the coefficient of thermal expansion of the fine-grained metallic coating with the one of the substrate minimizes dimensional changes during thermal cycling and prevents delamination.
Palumbo in U.S. Pat. No. 7,354,354 (2008), assigned to the same applicant, discloses lightweight articles comprising a polymeric material at least partially coated with a fine-grained metallic material. The fine-grained metallic material has an average grain size of 2 nm to 5,000 nm, a thickness between 25 micron and 5 cm, and a hardness between 200 VHN and 3,000 VHN. The lightweight articles are strong and ductile and exhibit high coefficients of restitution and a high stiffness and are particularly suitable for a variety of applications including aerospace and automotive parts, sporting goods, and the like.
Various patents address the use of electroplating to form grain-refined, metallic coatings on metallic substrates as a repair technique:
Palumbo in U.S. Pat. No. 5,516,415 (1996), U.S. Pat. No. 5,527,445 (1996) and U.S. Pat. No. 5,538,615 (1996) discloses a process for repairing degraded sections of metal tubes, such as heat exchanger tubes, by in situ electroforming a metallic layer on the inside of the tube. The electroformed structural layer has an ultrafine grain microstructure of sufficient thickness to restore the degraded section at least to its original mechanical specifications.
Palumbo in US2003/0234181A1 (2003) describes a process for in-situ electroforming a structural layer of metallic material to an outside wall of a metal tube for repairing an external surface area of a degraded section of metallic work pieces, especially of tubes and tube sections. Preferably, the metallic layer coatings are made of fine-grained metals, metal alloys or metal matrix composites. Also described is a process for plating “patches” onto degraded areas by selective plating including brush plating.